This works: (in-package :cl-user) (let* ((txt1 "hallo") (txt2 "yellow")) (cl-who:show-html-expansion (str nil :indent t) ((:a) txt1 txt2))) This does not work and hell breaks out when compiling: (defpackage :dummy-package (:use :cl :cl-user :cl-who)) (in-package :dummy-package) (let* ((txt1 "hallo") (txt2 "yellow")) (cl-who:show-html-expansion (str nil :indent t) ((:a) txt1 txt2))) ==> (LET ((STR STR)) (PROGN (WRITE-STRING " <a> " LET ((#:G1 NIL)) (WHEN #:G1 (PRINC #:G1 STR))) TXT1 (WRITE-STRING " " LET ((#:G2 NIL)) (WHEN #:G2 (PRINC #:G2 STR))) TXT2 (WRITE-STRING " </a>" LET ((#:G3 NIL)) (WHEN #:G3 (PRINC #:G3 STR))))) Well, I really don't get it with packages, so I just tried around and found that this code here works: (defpackage :dummy-package (:use :cl :cl-user :cl-who)) (in-package :dummy-package) (let* ((txt1 "hallo") (txt2 "yellow")) (cl-who:show-html-expansion (s nil :indent t) ((:a) txt1 txt2))) So kind-of it's not the package alone the problem, somehow it's the combination of package and using str in macro Ha, just tried with fmt instead of str: same problem Hint: Maybe no protection with gensym? And why does it work in cl-user?!? Using cl-who-0.11.1 And yes, I was in hell... And now (after changing str to s) I want just to understand what happend to me. thanks olli